1. Field of the Invention
This invention pertains to lighting fixtures and more particularly to an improved high mounted, side-window light fixture, which may be of the stacked variety.
2. Description of the Prior Art
Light fixtures housing sodium vapor, metal halide or other high intensity gaseous discharge lamps for providing general illumination to a large area, such as, for example, to a parking lot or an athletic playing area, are desirably mounted high above the area for long range lighting. However, the areas to be illuminated have corners, borders and the like. Universally reflecting light fixtures located in these positions provide light for the intended area, but also appreciable light from such fixtures is directed away from the intended area, which is not an efficient or productive use of light. Even light fixtures positioned in the middle of the area are relatively non-productive when a major portion of the light therefrom is projected upwards or straight out. That is, the most desirable light is generally outward and downward.
Moreover, light emanating from a fixture through a lens at a low angle undergoes a relatively larger amount of reflection back into the fixture than light emanating at a high angle. Therefore, by example, a light fixture with a bottom lens opening directs its most efficient light straight down. The light which exits at the exit pupil, on the other hand, is at the lowest angle of exit of any of the light and has, accordingly, a greater percentage of its light reflected at the lens than light reflected at the middle of the opening. Since the purpose of the high mounted light is to provide good general, wide-area ground illumination, it has been discovered that fixtures with vertical or side windows are generally the most suitable for this purpose. This is because for the light further out, the higher the angle through the window and the lesser is the amount of reflection. For the light closer in, the light is at a higher reflective angle, but the distance covered is less. Therefore, the overall brightness is generally satisfactory.
Also, it is often desirable to position more than one light fixture on a single tower or other installation to obtain maximum use of the number of installations that need to be made while increasing the number of fixtures in service, and hence the number of lamps, thereby making it possible to share ballast and other electronic components, as well as affecting the sharing of the mechanical installation components. When light fixtures are installed one on top of another, the installation is referred to as a "stacked fixture", which stack may include more than two lamp compartments.
One such stacked fixture structure is shown in U.S. Pat. No. 3,638,010, commonly assigned with the present application. In this structure, each compartment includes an upper and a lower reflector. The upper reflector is in two segments, each segment located generally over and outward from the lamp terminating at the top of a window. Light from the lamp is reflected outwardly and downwardly from a reflector segment through the adjacent window. There are windows on opposite sides of the compartment, hence light is reflected from the respective segments through both of these oppositely disposed windows.
The bottom curved reflector provides some secondary reflection from the lamp back to the top reflector segments to supply additional light downwardly and outwardly through the windows. However, because the reflector segments terminate near the top of their respective windows, there is a great deal of light from the light source that is unproductively projected outwardly but not downwardly, and some of which is even projected upwardly.
Light emanating from a lamp which is generally aligned with its elongate axis parallel with a parabolic reflector, the type of reflector which is generally desirable for producing parallel directed light rays from a fixture, produces a rather abrupt light change at the projection of the exit image.
It has long been known that by skewing a bulb in a cylindrical fixture so that the elongate axis thereof is not parallel with the edges of the window exit, sharp shadows can be greatly reduced. It has not been previously recognized that skewing a light bulb in a side-window fixture in such a manner so that the axis is not parallel with the plane of the window accomplishes the reduced shadow effect without detracting from the high reflective angle, light production discussed above.
Therefore, it is a feature of the present invention to produce an improved stacked fixture for emanating light outwardly and downwardly without wastefully directing light non-productively in other directions.
It is another feature of the present invention to provide an improved side-window fixture that eliminates abrupt changes of light at edges of light fixtures by placing the lamp therein at a skew angle with respect to the light fixture opening, thereby also reducing of fixture window size.